1. Field of the Invention
The present invention relates to a new copolyesteramide and a process for producing the same. More particularly, it concerns with a copolyesteramide composed of polyamide blocks obtained from a piperazine compound and an aromatic dicarboxylic acid and polyalkylene terephthalate blocks.
2. Description of the Prior Art
Aromatic polyesters such as polyethylene terephthalate and polybutylene terephthalate which are obtained from terephthalic acid and an aliphatic diol have found uses as fibers, films, and a variety of moldings on account of their outstanding mechanical properties, heat resistance, and chemical resistance. They can be improved in strength and elastic modulus by uniaxial or biaxial orientation, particularly in the case of fibers and films of polyethylene terephthalate. However, there has arisen a demand for a new polyester having higher strength and elastic modulus for use as tire cord and magnetic tape. There is also a demand for polyethylene terephthalate and polybutylene terephthalate having a higher glass transistion temperature or a higher glass transition temperature range, which is one of the indexes that determine their dimensional stability and usable temperature range, particularly the temperature at which the moldings produced therefrom lose their rigidity.
In order to meet such requirements, there was proposed in Japanese Laid-open Patent No. 65747/1979 an improvement through the blending of a rigid polymer. The proposed invention is disadvantageous in that a typical rigid polymer such as poly(p-phenyleneterephthalamide) can be readily blended with nylon, but not with an aromatic polyester, because it has a very high melting point or does not melt and there is no common solvent for both of them.
There is proposed in Japanese Laid-open Patent Nos. 125271/1979 and 123621/1980 a polyester having the aromatic amide unit. This polyester, however, is not greatly improved because the amide unit is not repeated consecutively. It is difficult to blend a polyester with an aromatic polyamide because the former has usually a very high melting point or does not melt and there is no common solvent for both of them. It is also difficult to copolymerize such an aromatic polyamide and a polyester.